Influencing factors and solutions to pitting corrosion in 316L stainless steel backwash pipelines

From the perspective of factors affecting pitting corrosion, the main factors leading to pitting corrosion in 316L stainless steel backwash pipelines are material, medium, flow rate and time. The medium cannot be changed, and the same applies to long-term stagnation. In the treatment and modification of backwash pipeline leaks, although drainage pipelines can be installed, the effect is not obvious because all seawater cannot be drained and completely dried, even if there is very little Seawater corrosion can still proceed in the direction of gravity at the bottom of the pipeline, and the increase in oxygen content in the solution and the evaporation and concentration of seawater will accelerate corrosion.
There are generally five basic ways to control corrosion, which are to use more suitable materials, improve the environment, use protective coatings, use cathodic protection or anodic protection, and optimize the design of systems or components. Among those that can be adopted are the reuse of materials and the use of protective coatings. Using external cathodic current protection can inhibit pitting corrosion of 316L stainless steel, but this is more expensive and will aggravate corrosion of nearby unprotected metal parts.
Therefore, an effective way to solve pitting corrosion in backwash pipelines is to consider enhancing the corrosion resistance of the inner wall of the pipeline. In the actual on-site transformation, the method of carbon steel pipes and vulcanized rubber lining was used.
First, all stainless steel pipes were dismantled, and the on-site design was to flange-connect carbon steel pipes based on the original pipeline paths. Among them, the rubber-lined pipes cannot be welded. Then the carbon steel pipes are processed on site and sent to the rubber lining manufacturer. The inner and outer surfaces of carbon steel pipe sections are sandblasted in the rubber lining factory. Next, the outer surface is coated with anti-rust primer, and the inner surface is manually lined with rubber skin. Carry out electric spark inspection on the rubber lining to ensure the continuity of the rubber lining, and use epoxy resin to repair individual defective points; vulcanize and fumigate the rubber to harden the rubber lining; use rubber pads for flange connections during installation. The bolts are galvanized bolts with anti-corrosion coating. After installation, the pipe surface is coated with anti-corrosion topcoat.
In addition to the above methods, duplex stainless steel can also be used. At present, with the continuous improvement of technical level, duplex stainless steel that can resist chloride ion corrosion is developing rapidly. Duplex stainless steel is to add a certain content of molybdenum to stainless steel and add chromium elements with a higher chromium content than austenitic stainless steel. This can make duplex stainless steel achieve better resistance to chloride pitting and crevice corrosion. In the second generation of duplex stainless steel, nitrogen is added to the duplex stainless steel to promote the formation of austenite and improve tensile properties and pitting corrosion resistance.